Over in the New York Times Andy Revkin has a piece discussing the way that the general scientific view is that climate sensitivity is lower than many had previously assumed. This is good news of course: but one of the implications seems not to have occurred to people yet. This makes climate change itself a much cheaper problem to deal with.

Climate sensitivity is how much will the temperature change over a doubling of atmospheric CO2 (more strictly, CO2-e, taking account of methane and all the other gasses and converting them to CO2 equivalents). No, not how much it will change first and then go haywire because of all the feedbacks: how much will it change in total? There have been some pretty extreme estimates out there: up to 11 oC according to some people. Very few people and no one pays all that much attention to them, true, but they're out there. Most of the science in this areas seems to be saying under 4.5 oC. And the estimates keep getting a little lower. As James Annan, one of the experts in the field says:

A value (slightly) under 2 is certainly looking a whole lot more plausible than anything above 4.5.

And here's the importance of this. The lower climate sensitivity is the cheaper it is going to be to deal with it. Of course, if it's zero then there's no cost at all for we won't have to do anything. But that's more than somewhat unlikely. What a lower but still positive sensitivity does is gives us more time to deal with emissions. And the more time we have the cheaper it all becomes for two reasons.

The first is to do with the capital cycle. Say that we do indeed want to move from fossil fuels to renewables. Clearly this is cheaper if we can use our current fossil plants until they need replacing anyway. Then we build the renewables plants. The alternative, building the renewables right now and then closing down perfectly functional fossil plants of obviously more expensive. We lose that capital value of those plants we've closed down early. If sensitivity really was 11 oC then I'd be right there saying Dang The Cost, get them closed down now. At 3 oC, or 2 even, then we just don't need to waste money in that manner. We've decades in which to make the switch over.

The second is that renewables aren't really quite ready for prime time yet. They're still more expensive than fossil fuels except in certain highly specific locations. That's why we still have to subsidise them. If we've more time because there's a low sensitivity then we don't actually need to install the current generation of tee expensive renewables. We can simply wait and install the next, or the one after that, whenever it is that we get to true, unsubsidised, cost benefits. With solar this is only a few years away. With windmills I'm not entirely certain that it will ever be reached. With fuel cells I'd put it at 15 years perhaps. Low sensitivity means we've got the time to wait for these technologies to mature.

Another way of putting this same point is that yes, even with a low sensitivity we did need to do something to beat climate change. But a low sensitivity means we've already done it in large part. The billions upon billions that have been thrown at renewable technologies haven't produced a truly price competitive technology yet. But I think that it's entirely obvious that the next iteration or two of some of them will indeed be. At which point of course we'll all quite naturally start using them. As those old fossil fuel plants need replacing if solar or fuel cells are cheaper then we just won't build new fossil plants: we'll build solar or fuel cell ones. At which point dealing with climate change costs us nothing at all.

I wouldn't say that it is now obvious that climate change is solved: there's still too much uncertainty about what that sensitivity is for that as yet. But the lower that sensitivity is the more it looks like we've already put in place the policies needed to deal with it. If we have some decades then the work that's already being done on renewables will bear fruit and we'll all naturally switch to them as they become cheaper than fossil fuels.